By the way, I've been playing with tweaks and variations of this, and I think this is _pretty much_ the canonical way to do this ride:
Though in Dumbo I had to dodge around some construction vehicle slowdowns.
Anyway, this bags *4* boroughs rather than 3 (by touching a toe into Mott Haven). It does indeed use the Bk Bridge and Hudson River Greenway rather than 1st ave. It also adds a jaunt to the northern bikeable limit of the Queens waterfront near the outset, and in the wind-down it finds a buttery way past the Manhattan/Bk Bridge landing area to get down to Atlantic Ave, then back up. It uses the stairs approach to the Bk Bridge on the Bk side rather than the plaza approach; I've found that one tends to wait at the traffic lights on Tillary for an unbuttery length of time if so.
So, sf2g riders, if you find yourself in NYC some time, HMU and I'll ride this with you. :-)